The thymus leukemia antigen (TLa) and CD1 are mouse, nonclassical class I molecules that are expressed on intestinal epithelial cells. The function of these molecules is unknown, and a cell-mediated immune responses directed to either TLa or mouse CD1 have not been reported. However, on account of their location, it is possible that TLa and CD1 present peptide to intestinal intraepithelial lymphocytes (IEL). Based upon our preliminary data, we further hypothesize that these nonclassical class I molecules can acquire peptide outside of the endoplasmic reticulum, and that they have evolved to present peptides from intestinal pathogens that replicate in sites such as endosomes or phagolysosomes. To better understand the function of TLa and CDI, and their possible role in the mucosal immune response, experiments will be performed to compare the behavior of these molecules to classical class I proteins. Cell adhesion and binding assays will be carried out to determine if TLa and CDI can interact with CD8, a co-receptor which is expressed by most IEL in the small intestine. We will also determine if TLa and CDI require beta2microglobulin for their surface expression. Peptides bound by transfected cells that express these molecules will be eluted and sequenced to determine if there is a required anchor motif. Because both of these nonclassical class I molecules are stably expressed in RMA-S cells that lack peptide antigen transporter, cell trafficking studies will be performed to determine where peptide may be acquired. These experiments therefore will determine if TLa and CDI have antigen presenting function, and the types of antigens that they present. The results obtained from these studies can then be applied to studies investigating the possible in vivo function of TLa and CDI. We will focus on three areas. First, we will determine the HPLC profile of peptides eluted from TLa and CDI expressed by intestinal epithelial cells, to determine if there are major differences compared with the transfectants. Second, using transgenic mice that express TLa on all their tissues, we will attempt to raise TLa-restricted T-cell lines. Studies on these lines can determine directly the requirements for antigen presentation by TLa. Third, the ability of IEL to recognize peptides bound by TLa and CDI will be determined. These studies should provide important insights into antigen presentation function in the gut, which may provide further insight into oral tolerance induction and mucosal immune dysfunction such as in inflammatory bowel disease.